In the interconnection of shafts for the joint rotation thereof or torque transmission therebetween, elastic or flexible couplings are generally provided to compensate for inexact alignment of the shaft axis and to absorb perturbations in the torque transmission therebetween.
While such devices are known in various constructions and configurations, an important number of them are of the so-called disk type wherein a rigid annular inner member is affixed to one shaft, a rigid annular outer member is affixed to the other shaft and the two members are bridged by an annular flexible element, e.g. of an elastomeric material such as rubber, such that the two members and the element are generally coplanar. The two members are angularly fixed to the respective shaft, i.e. rotate therewith.
In one conventional construction of this type, the inner coupling half or member is provided with a rigid shoulder to which the elastomeric member is clamped while the external periphery of the elastomeric member is toothed and engages in an array of internal teeth of, for example, a flange ring affixed to a motor flywheel.
A disadvantage of the clamping of the elastomeric coupling element in the region of its inner diameter is the reduction in the effective elastic length, i.e. the radial dimension of the element over which it remains yieldable, thereby increasing the tendency to wear and introducing problems of force transmission in the transition zones. Since the coupling element is subjected to varying force conditions, its life is limited.
It is also a disadvantage that the clamping arrangement is difficult to accomplish in some cases and contributes to a high cost of the coupling. Since the only connection along the outer periphery is with arrays of teeth which can have play between them, wear at this point is also a problem and there is always a danger that the teeth of the elastomeric element may jump past the teeth of the outer coupling member.
To avoid these problems it has also been proposed to vulcanize a rubber ring to inner and outer rigid rings, thereby forming the coupling. While this construction is indeed simpler and avoids the problems which arise with clamping systems, the double-sided vulcanization of the elastomeric coupling element to the inner and outer rings is relatively costly.
Furthermore, and possibly of even greater importance, is the fact that vulcanization of the elastomeric element to the inner and outer rigid members of the coupling greatly limits the degree of angular adjustability between the two members and the angle through which the two members can be relatively twisted within the elasticity limits of the elastomeric member.
Additionally, experience has shown that the limiting stress is rapidly reached with relatively small angular offsets of the two members thereby reducing the versatility of the device.
In order to increase the angular offset which can be sustained without exceeding the elastic limit of the elastomeric member, it has been proposed to provide a coupling with a plurality of elastic elements each being disposed between a rigid inner ring and a rigid outer ring so that the space between inner and outer members contains several elastomeric rings separated from one another by rigid rings to which the elastomeric rings are vulcanized in a concentric manner.
Where vulcanization to intermediate rings is provided, the contact surfaces may be frustoconical and of opposite convergence with the elastomeric elements being clamped to the ring by axial forces. Because of the frustoconical surfaces and the axial pressure, the elastomeric elements may be under radial prestress which increases the durability of the elastomeric element and permits the desired angular offset to be sustained. The key disadvantages of such arrangements are the large number of vulcanization joints and their high cost of fabrication and the complexity of forming the coupling and installing same. In general, such shaft couplings are prohibitively expensive.
Finally, mention may be made of an elastic shaft coupling in which the elastomeric coupling element, which is not under prestress, has a frustoconical configuration. This type of coupling does not provide an angular offset which is sufficiently large for all purposes, especially when it is of compact configuration and has the characteric that torques applied to it are converted into axial forces which are disadvantageous and to be avoided.